1. Field of the Invention
The present invention relates to a resist composition for immersion exposure (liquid immersion lithography), a method of forming a resist pattern that uses the resist composition for immersion exposure, and a fluorine-containing compound useful as an additive for a resist composition for immersion exposure.
Priority is claimed on Japanese Patent Application No. 2008-163861, filed Jun. 23, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or an electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
For miniaturization of semiconductor devices, shortening of the wavelength of the exposure light source, and increasing of the numerical aperture (NA) of the projector lens have progressed. Currently, exposure apparatuses in which an ArF excimer laser having a wavelength of 193 nm is used as an exposure light source and NA=0.84 have been developed. As shortening of the wavelength of the exposure light source progresses, it is required to improve various lithography properties of the resist material, such as the sensitivity to the exposure light source and a resolution capable of reproducing patterns of minute dimensions. As a resist material which satisfies these conditions, a chemically amplified resist is used, which includes a base resin that exhibits a changed solubility in an alkali developing solution under action of acid and an acid generator that generates acid upon exposure.
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are typically used as base resins for chemically amplified resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm.
Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.
As a technique for further improving the resolution, a lithography method called liquid immersion lithography (hereafter, frequently referred to as “immersion exposure”) is known in which exposure (immersion exposure) is conducted in a state where the region between the objective lens of the exposure apparatus and the sample is filled with a solvent (an immersion medium) that has a larger refractive index than the refractive index of air (see for example, Non-Patent Document 1).
According to this type of immersion exposure, it is considered that higher resolutions equivalent to those obtained using a shorter wavelength light source or a larger NA lens can be obtained using the same exposure light source wavelength, with no lowering of the depth of focus. Furthermore, immersion exposure can be conducted using a conventional exposure apparatus. As a result, it is expected that immersion exposure will enable the formation of resist patterns of higher resolution and superior depth of focus at lower costs. Accordingly, in the production of semiconductor devices, which requires enormous capital investment, immersion exposure is attracting considerable attention as a method that offers significant potential to the semiconductor industry, both in terms of cost and in terms of lithography properties such as resolution.
Immersion lithography is effective in forming patterns having various shapes. Further, immersion exposure is expected to be capable of being used in combination with currently studied super-resolution techniques, such as phase shift methods and modified illumination methods. Currently, as the immersion exposure technique, a technique using an ArF excimer laser as an exposure source is being actively studied, and water is mainly used as the immersion medium.
In recent years, fluorine-containing compounds have been attracting attention for their properties such as water repellency and transparency, and active research and development of fluorine-containing compounds have been conducted in various fields. For example, in the fields of resist materials, currently, an acid-labile group such as a methoxyethyl group, tert-butyl group or tert-butyloxycarbonyl group is being introduced into a fluorine-containing polymeric compound, and the fluorine-containing polymeric compound is used as a base resin for a chemically amplified positive resist. However, when such a fluorine-containing polymeric compound is used as a base resin for a chemically amplified positive resist, disadvantages are caused in that a large quantity of out gas is generated following exposure, and the resistance to dry etching gases (namely, the etching resistance) is unsatisfactory.
Recently, as a fluorine-containing polymeric compound exhibiting excellent etching resistance, a fluorine-containing polymeric compound having an acid-labile group containing a cyclic hydrocarbon group has been reported (see, for example, Non-Patent Document 2). In addition, a fluorine-containing polymeric compound has been reported in order to provide a resist film with water repellency in a resist composition for immersion exposure (see, for example, Non-Patent Document 3).    [Non-Patent Document 1] Proceedings of SPIE (U.S.), vol. 5754, pp. 119-128 (2005)    [Non-Patent Document 2] Proceedings of SPIE (U.S.), vol. 4690, pp. 76-83 (2002)    [Non-Patent Document 3] Journal of Photopolymer Science and Technology, Vol. 19, No. 4, pp. 565-568 (2006)